Motor protector with metal housing and with preformed external heater thereon

ABSTRACT

A motor protector has a thermally responsive contact element mounted inside a flat, rectangular, open-ended metal can. A metal cover mounts a complementary contact and is secured over the open end of the can by can flanges to clamp an electrically insulating gasket between the can and cover. The contact means close a circuit between the can and cover but the thermally responsive contact element is movable in response to increase in temperature for opening that circuit. Integral crimpable terminals are provided on the can and cover. A flat metal heater ribbon having an insulating coating thereon has one end welded to the exterior of the can. The ribbon coating is deformed at selected locations and the coated ribbon is folded at those locations to fit closely against the three exterior sides of the flat rectangular can. The can terminal crimps the opposite end of the coated ribbon in electrically insulated relation to the ribbon for holding the coated ribbon in position on the can. In that way, the heater is adapted for automated assembly on the can to provide consistent uniform heat-transfer to the can. The heater is also disposed to be easily and reliably connected in series with the contact means in a motor circuit for improving the thermal response, cost and service life characteristics of the motor protector.

In some motor protector systems where consistent mounting of a motorprotector in efficient heat-transfer relation to a motor winding cannotbe assured, or where prompt anticipation of overheating of a motorwinding is desired, an electrical resistance heater is connected inseries with the motor winding and is arranged in predeterminedheat-transfer relation to the thermally-responsive component of themotor protector. The heater is responsive to the occurrence of theoverload or other fault currents in the winding for heating the thermalcomponent of the protector to open the motor circuit before excessiveoverheating of the motor winding can take place.

In a previously known motor protector of that type as shown in U.S. Pat.No, 4,086,558, the basic protector structure is adapted for automatedmanufacture and the heater is disposed with a selected orientation onthe exterior surface of the basic structure. In that arangement, thebasic protector is made at low cost and a heater of desired proportionscan be added outside the basic structure to adapt the motor protectorfor use with motors of various different sizes and ratings. Further,because the heater is mounted externally, it is proportioned to heat thesubstantial thermal mass of the protector when interrupting the motorcircuit in response to the occurrence of an overload or other faultcurrent condition in the motor. The protector then keeps the motorcircuit open for a subsantial period of time while the relatively largemass of the protector cools before the protector permits the motorcircuit to reclose. That is, the protector cycles only at a relativelyslow rate while the fault condition persists so that the protector tendsto display a very long service life.

However, it is found that the external heater is difficult to mount onthe mass-produced, basic structure of the protector and does not alwaysdisplay uniform heat-transfer to the basic protector structure. Further,connection of the previously known protector in a motor circuit isdifficult and somewhat unreliable. Most important, the assembly of theexternal heater adds significantly to the cost of the otherwiseinexpensive motor protector unit.

It is an object of this invention to provide a novel and improved motorprotector; to provide such a protector which is readily adapted forprotecting motors of different sizes and ratings, which is promptlyresponsive to the occurrence of fault currents in a motor windingcircuit, which displays improved cycle time and service life, and whichis particularly useful in protecting motors with relatively low motorcurrent or motors having high rates of temperature rise under faultcondition; to provide such a motor protector which is adapted forautomated manufacture of the basic protector structure and assembly of aproperly proportioned, exteriorly mounted heater on that structure; andto provide such a motor protector having an exteriorly mounted heaterwhich is securely and reliably mounted on the heater for convenientconnection in a motor winding circuit.

Other objects, advantages and details of the novel and advantageousmotor protector of this invention appear in the following detaileddescription of preferred embodiments of the invention, the detaileddescription referring to the drawings in which:

FIG. 1 is a plan view of the motor protector provided by this invention;

FIG. 2 is an end elevation view of the protector of FIG. 1;

FIG. 3 is a section view along line 3--3 of FIG. 1; and

FIG. 4 is a bottom plan view of the device of FIG. 1.

Referring to the drawings, 10 in FIGS. 1-4 indicates the novel andimproved protector of this invention which is shown to include a basicmotor protector assembly 12 incorporating a fixed electrical contact 14mounted in a metal housing 16 and a complementary electrical contact 18movable along an axis (indicated at 22 in FIG. 3) by a thermostaticbimetallic element 20 to engage and disengage the first contact 14 inresponse to changes in the temperature of the thermostatic element. In apreferred embodiment of this invention, the basic protector assembly 12is particularly adapted to be mass produced at very low cost and thethermal mass of the housing and electrical contacts embodied in theassembly is large relative to the thermal mass of the thermostaticelement in the assembly.

Typically, for example, the basic motor protector assembly 12corresponds to that shown in U.S. Pat. No. 3,430,177 issued on Feb. 25,1979 to R. T. Audette. That is, as is illustrated in FIGS. 1-4, thehousing 16 of the assembly 12 preferably comprises a flat metal plate 24having an integral, crimpable terminal sleeve 24.1 at one end of theplate. The first contact 14 is welded to the plate 24 as shown in FIG.3. A sheet 26 of gasket material has a main portion 26.1 fitted over theplate, has an opening 26.2 in the main portion of the gasket fittedaround the contact 14, and has edges 26.3 extending around respectivelateral edges of the plate 24. The housing 16 further includes a flat,rectangular, open-ended can member 28 having a bottom 28.1, side walls28.2, 28.3, 28.4 and 28.5, a flange 28.6 extending from the side walls,an integral, crimpable sleeve terminal 28.7 extending from the flange atone end of the can, and a pair of tabs 28.8 extending from aroundrespective edges 26.3 of the gasket and around the lateral edges of thecover plate 24 to grip and secure the cover plate 24 in sealed,electrically insulated relation to the can. The thermostatic element 20is welded to the can bottom 28.1 by means of a welding slug 30 to extendin cantilever relation from the can bottom. The movable, complementarycontact 18 is welded to the distal end of the element 20 as shown inFIG. 3. As will be understood, the thermostatic element 20 is formed oftwo layers of metal of different coefficients of thermal expansion andhas a dished or non-developable portion 20.1 intermediate its end. Withthis construction, the element 20 normally holds the movable contact 18in engagement with the fixed contact 14 to close a circuit between thecover 24 and the can 28. However, when the element is heated to aselected temperature, the element moves, with snap-over-center action ofthe dished portion thereof, to the disposition indicated by the brokenline 20a in FIG. 3, thereby to disengage the contacts to open the notedcircuit. Typically, the materials of the thermostatic element areselected to provide the element with a desired electrical resistivity sothat the element is heated to a selected extent by the flow ofelectrical current through the element. As the basic assembly 12 isconventional, it is not further described herein and it will beunderstood that the element 20 is adapted to move with snap-action todisngage the contacts when the element is heated to a first selectedtemperature and is then adapted to move with snap-action to reengage thecontacts when the element subsequently cools to a second, relativelylower, element temperature. Preferably, in a typical embodiment of thisinvention, the basic protector assembly 12 is about 0.750 inches long,0.375 inches wide and about 0.187 inches thick. Further, thethermostatic element 20 typically has a mass of approximately 0.05 gramswhereas the combined mass of the housing, contacts and other metalcomponents of the assembly is typically on the order of 1.4 grams.

In accordance with this invention, the motor protector 10 includes aheater element 32 having a thin, flat, metal, heater ribbon 34 formed ofa nichrome alloy or the like having selected electrical resistanceproperties. A coating 36 of an electrical insulating material such astetrofluoroethylene (Teflon) or the like is provided on the ribbon whilethe ends 34.1 and 34.2 of the ribbon are free of the coating. The ribboncoating is deformed at selected locations 36.1 as indicated in thedrawing so that the heater element readily folds at those locations toconform to the three exterior side walls of the flat, rectangularhousing can 28 to be mounted in close heat-transfer relation to the can.Preferably for example the resistance heater ribbon 34 is provided in acontinuous coil with the coating 36 extruded onto the ribbon in anyconventional manner. The heater element 32 is cut from that coil to thedesired length and the coating is stripped from the ends 34.1 and 34.2of the metal ribbon. The coating is also deformed under pressure at twolocations 36.1 so that the coated ribbon folds and lays snugly andeasily against the three exterior sides 28.3-5 of the housing can. Theribbon end 34.1 is welded to the can side 28.5 as shown at 38 in thedrawing so that it is electrically connected to the can and is securelyattached to the can. The other end of the heater element is thenextended through the can terminal 28.7 which is crimped against theheater element coating for holding the heater in position on the can.That is, the weld of one end end 34.1 of the ribbon to the can locatesthat end of the ribbon relative to the can so that the heater elementreadily folds at the location to lay closely against the exterior sides28.3-5 of the housing can. With the heater element pulled to lay againstthe can sides, the can terminal 28.7 is crimped to the element coatingin electrically insulated relation to the heater ribbon 34. In that way,the terminal 28.7 secures the heater element in its assembled positionon the can and disposes the stripped end 34.2 of the heater element in aposition to be easily connected in an electrical circuit. In typicalembodiments of the invention, the heater ribbon has a thickness of about0.005 to 0.010 inches and a width of about 0.070 inches and is formed ofa nichrome alloy or other material selected to provide the ribbon with apredetermined resistance in the range from about 0.005 to 0.550 ohms asmay be desired. The coating 36 has a typical thickness on the order of0.020 inches at the sides of the ribbon.

In that arrangement, when the cover terminal 24.1 and the end 34.2 ofthe heater ribbon are connected in series with a motor winding (notshown), the winding current is directed through the heater 32, the can28, the thermally responsive element 20, the contact 18, the contact 14,the cover 24 and the cover terminal 24.1. When an overload or otherexcessive fault-condition current flows in the motor winding, heat isgenerated in the heater 32 for moving the thermally responsive element20 to open the motor winding circuit as will be understood. Because theheater 32 is in series with the can and cover and the thermallyresponsive element 20, current flow in all of those componentscooperates in generating sufficient heat to actuate the element 20 whenan overload current occurs in the motor winding, and, because the heater32 is externally mounted on the basic protector structure 12, the heateris proportioned to generate a selected amount of heat in response to apredetermined overload current for opening the winding circuit in adesired period of time.

In the protector 10 as above described, the heater coil is oriented withits coil axis parallel to the axis 22 as discussed in U.S. Pat. No.4,086,558. The heater characteristics are easily modified by providingheater ribbon 34 of various alloys, widths and thicknesses to generatethe desired level of heat but the ribbon is adapted to be inexpensivelymounted on the basic structure 12 by any of various conventionalautomated assembly techniques. Mouting of the heater having the notedconfiguration is adapted to provide consistent heat-transfer to thehousing can 28 and to the element 20 within the can. The heater issecurely mounted on the can 28 and the terminal 24.1 and the heater end34.2 are conveniently disposed to be easily and reliably connected in amotor winding circuit.

It should be understood that although particular embodiments of themotor protector 10 are described by way of illustrating this invention,the invention includes all modifications and equivalents of thedisclosed embodiments falling within the scope of the appended claims.

I claim:
 1. A thermally responsive motor protector comprising arectilinear metal housing having a body component and a cover componentsecured together in electrically insulated relation to each other toform an enclosure, thermally responsive means mounted within theenclosure normally closing a circuit between the body and cover andmovable when heated to a selected temperature for opening that circuit,and a heater having a flat ribbon of metal of selected electricalresistance properties having a deformable electrically insulatingcoating covering a central portion of the ribbon, said coating beingdeformed at selected locations and being folded at said locations fordisposing selected portions of the metal ribbon in heat transferrelation to selected rectilinear portions of said housing, said ribbonhaving one end thereof electrically connected to one of said housingcomponents and having its opposite end disposed to be connected in anelectrical circuit.
 2. A protector as set forth in claim 1 wherein saidhousing body comprises a flat, rectangular, open-ended metal can andsaid heater has one end welded to said can.
 3. A protector as set forthin claim 1 wherein said can has integral means supporting the oppositeend of said heater.
 4. A thermally responsive motor protector comprisinga flat, rectangular, open-ended metal housing can having a bottom, fourside walls upstanding from the bottom, a flange on the side wallsextending around the open end of the can, and an integral crimpableterminal on the flange, a metal cover secured in electrically insulatedrelation to the can over the open end of the can forming a housingenclosure, the cover having an integral terminal thereon, thermallyresponsive means mounted within the enclosure normally closing a circuitbetween the can and cover, the thermally responsive means being movablewhen heated to a selected temperature for opening said circuit, andelectrical resistance heater means mounted exteriorly of the housingenclosure to be connected in series with the can and cover and with amotor winding for heating the thermally responsive means to open saidcircuit and interrupt current flow in the winding in response to theoccurrence of an overload current in the winding, characterized in thatthe heater comprises a flat ribbon of metal of selected electricalresistance properties having a deformable electrically insulatingcoating thereon, said coating being deformed at selected locations andbeing folded at said locations to dispose portions of the heater snuglyagainst receptacle side wall portions of the can in selected, uniformheat-transfer relation to the thermally responsive means within saidenclosure, said metal ribbon having one end welded to one of said sidewalls for securing the ribbon in electrically connected relation to thecan and said heater having a coated portion adjacent its opposite endcrimped in said can terminal in electrically insulated relation to thecan for disposing the opposite end of ribbon to be connected to saidmotor winding.